Granted this is from a quick nUI test, but I had got it working for Legion Beta, so assume these were changed in Battle For Azeroth. nUI on Login resulted in 33 unique error messages, some were these events, others what appeared to be Blizzard functions and the rest nUI functions.

This is an event that flagged up as missing when testing my mage portals addon
>Attempt to register unknown event "PARTY_CONVERTED_TO_RAID"

These came up while logging in with Titan Panel ( and its built in modules activated ) so I could test my Alt ILevel Addon
>Attempt to register unknown event "MINIMAP_ZONE_CHANGED"
>Attempt to register unknown event "PARTY_MEMBERS_CHANGED" ---- Same as above
>attempt to index global 'WorldStateAlwaysUpFrame' (a nil value)

And my Alt ILevel addon came up with this one
>Attempt to register unknown event "PLAYER_AVG_ITEM_LEVEL_READY"

Thank you Fizzlemizz and Xrystal for linking to my observations and my GitHub

Please note that I have also started updating the API changes article on Wowpedia with the things I am able to test and confirm in-game. If you can, please consider participating in this article to gather all the changes.

The changes are really not that bad. Most come down to removing the spell rank from all sorts of places and in some cases also going away from spell name in favor of spellID. All of those are relatively easy to fix.